In many applications, such as in the production of semiconductors, vertically movable machine elements must be retained counter to the force of gravity and be precisely positioned in the process. The required operating range of a few millimeters is frequently relatively low, but the demands on the positioning accuracy therefore all the higher. Positioning accuracy in the micrometer range and below may be required.
European Published Patent Application No. 2 034 593 describes a vertical actuating drive, which utilizes reluctance forces between a movable and a stationary component in order to compensate for the force of gravity of the movable component in the operating range of the actuator drive, so that the movable unit assumes a stable position above the operating range in the event that a linear motor controlling the vertical movement is switched off or malfunctions.
PCT International Published Patent Application No. WO 2009/093907 describes actuator drives which utilize a combination of a mechanical and a magnetic spring. In this case, the gravity of a movable component is able to be compensated by the spring forces, the spring constants of the two springs canceling each other out, thereby providing for force-free shifting of the movable component within the operating range of the actuator drive. This also prevents the transmission of vibrations between the stationary and movable subassemblies, which has an advantageous effect on the precise positioning. PCT International Published Patent Application No. WO 2009/093907 describes providing the mechanical spring as a flat spring, so that guidance is provided for the movable component in the vertical direction.